AC Milan have angered Everton by announcing the loan signing of Gerard Deulofeu despite no agreement being reached between the clubs.
Press Association Sport understands officials at Goodison Park are "fuming" at the Serie A club's actions.
Negotiations have been ongoing for the last 10 days but, with no deal having been struck, the Italian club have jumped the gun.
The Rossoneri, via their official Twitter account, claimed the former Barcelona prodigy - who has made just 13 appearances since the summer arrival of manager Ronald Koeman - had completed a temporary move until the end of the season.
And while Koeman admitted on Thursday he was open to letting the Spain international leave Goodison Park on a temporary basis should the right offer come along, that has not yet happened.
The 22-year-old winger has been in and out of the Everton side since joining on a permanent basis in summer 2015, following a previous successful loan spell in 2013-14, and has made just 46 appearances since arriving from Barca.
However, he has struggled for game-time this season, with Koeman acknowledging he may need to leave for more regular action.
"I spoke to Geri and it's a difficult situation for the player," the Dutchman said.
"If he finds a solution to go and to play and to get game-time then it's not a problem.
"You have to always look for first what's the best for the club and second what is the best for the player, and for Geri the best is that he gets game-time somewhere."